Hyperthrophic Pyloric Stenosis Flashcards
What is hypertrophic pyloric stenosis (HPS)?
HPS is a thickening of the pyloric muscle in neonates causing stomach outlet obstruction. The exact cause is unknown.
How does the pathophysiology of hypertrophic pyloric stenosis progress?
- The pyloric muscle hypertrophies over a few days to weeks.
- Gastric outlet obstruction worsens until there is no passage of content into the duodenum.
- The stomach dilates.
- Milk vomits worsen and become projectile, but the child remains hungry.
- Peristalsis becomes stronger and can be seen on the anterior abdominal wall.
What are the signs of hypertrophic pyloric stenosis in a neonate?
- Projectile vomiting.
- Persistent vomiting leading to failure to thrive initially.
- Eventually, marked wasting and severe electrolyte derangements.
- Visible peristalsis on the abdominal wall.
What electrolyte imbalances occur in hypertrophic pyloric stenosis?
• Hypochloraemia
• Hyponatraemia
• Hypokalaemia
• Marked metabolic alkalosis
• Occasional unconjugated hyperbilirubinaemia.
How does vomiting in hypertrophic pyloric stenosis affect electrolyte levels?
Vomiting causes loss of hydrogen ions, sodium, and chloride. This results in hypochloraemia, hyponatraemia, and hypokalaemia, along with a marked metabolic alkalosis.
What causes the paradoxical aciduria in hypertrophic pyloric stenosis?
The low serum potassium during severe dehydration leads to potassium moving into cells. Potassium is also preferentially retained in the kidneys via the K+/H+ pump, resulting in hydrogen ion loss in the urine despite the patient being already alkalotic. This leads to paradoxical aciduria.
What is the incidence of hypertrophic pyloric stenosis?
The incidence is reported to be as high as 1:1000 live births.
What percentage of hypertrophic pyloric stenosis cases have a family history?
A family history is present in 5-20% of patients.
What is the gender distribution of hypertrophic pyloric stenosis?
Hypertrophic pyloric stenosis occurs more commonly in males, with a male-to-female ratio of 4:1.
In which birth order is hypertrophic pyloric stenosis more common?
It is more common in the first-born child.
Which population has a higher incidence of hypertrophic pyloric stenosis?
It is more common in the Caucasian population.
What is the classic presentation of hypertrophic pyloric stenosis?
The classic presentation is a 6-week-old male with milk vomiting starting from 2 to 3 weeks after birth. The vomiting becomes larger, more frequent, more forceful, and eventually projectile immediately after a feed.
What are the common signs in a baby with hypertrophic pyloric stenosis?
• The baby cries a lot.
• Feeds eagerly.
• Rapid weight loss.
What is a potential complication in hypertrophic pyloric stenosis that causes vomiting?
Haematemesis (coffee-ground vomits) may occur in about 15% of cases due to gastritis from old milk curds irritating the gastric mucosa, as well as oesophagitis from secondary gastro-oesophageal reflux.
What is the general appearance of a baby with hypertrophic pyloric stenosis during examination?
The baby appears wasted with no signs of sepsis.
What is the dehydration status in babies with hypertrophic pyloric stenosis?
Many babies are 5 to 10% or more dehydrated.
What percentage of babies with hypertrophic pyloric stenosis are jaundiced?
About 2% of babies with hypertrophic pyloric stenosis are jaundiced due to impaired glucuronyl transferase activity with fasting.
What can be observed in the epigastric area of babies with hypertrophic pyloric stenosis in advanced cases?
In advanced cases, visible waves of gastric peristalsis can be seen after a feed in the epigastric area.
What is the condition of the abdomen during examination?
The abdomen is soft and non-tender.
What is observed during vomiting in babies with hypertrophic pyloric stenosis?
Projectile vomiting of stomach contents may be observed.
How is the ‘Pyloric Tumour’ or ‘olive-shaped’ mass palpated?
The mass can be palpated in about 50% of cases on the right border of the right rectus muscle just above the umbilical level. The baby should be relaxed, either in the caregiver’s arms or lying on its right side after a test feed. The examiner stands on the left side and palpates deeply for the mass.
What investigations are required to assess the degree of metabolic derangement in hypertrophic pyloric stenosis?
Urea and electrolytes as well as venous gas are required to assess the degree of metabolic derangement.
What is the diagnostic investigation for hypertrophic pyloric stenosis?
Ultrasound is the diagnostic investigation, with nearly 100% sensitivity. The length, width, and thickness of the pyloric muscle are measured.
What measurements of the pyloric muscle on ultrasound are considered diagnostic for hypertrophic pyloric stenosis?
• Muscle thickness >5mm
• Width >10mm
• Length >15mm
Is abdominal x-ray needed for the diagnosis of hypertrophic pyloric stenosis?
Abdominal x-ray is often done but is not needed and should generally not be performed. If done, it may show a large distended stomach with a frothy air-fluid level and minimal distal gas.
When is a contrast meal performed in hypertrophic pyloric stenosis, and what are its findings?
A contrast meal is not typically needed, but if the ultrasound is atypical despite typical metabolic derangements, it may be performed. It can show:
• A long, narrow pyloric canal with a ‘string sign’
• Pyloric shouldering or the “mammary” sign.
What is the first step in managing hypertrophic pyloric stenosis?
The first step is to correct dehydration and metabolic derangements.
How is dehydration typically corrected in hypertrophic pyloric stenosis?
Dehydration is corrected with:
• Nasogastric tube for feeding.
• Intravenous fluid therapy, starting with fluid boluses of normal saline.
What is the goal for urine output in hypertrophic pyloric stenosis management?
A urine output of 1 ml/kg/hour should be achieved.
What fluids are used for maintenance after initial rehydration in hypertrophic pyloric stenosis?
Maintenance fluid and electrolyte replacement includes:
• “Half normal saline” (0.45% NaCl) with KCl and 5% dextrose.
• Fluid is given at 130-150% of normal maintenance infusion rate, i.e., 180-220 ml/kg/day.
Why is sodium level monitoring important during management of hypertrophic pyloric stenosis?
There is a risk of pontine demyelination if sodium is raised too quickly, so regular blood sodium monitoring is important, especially if normal saline is being administered.
What is the operation of choice for correcting hypertrophic pyloric stenosis?
The operation of choice is the Ramstedt Pyloromyotomy, which can be performed either open or laparoscopically.
When should surgery be performed in hypertrophic pyloric stenosis?
Surgery is performed once electrolytes and pH have normalized, which may take 1 to 5 days.
What are the risks of surgery if the pH, chloride, or bicarbonate levels are abnormal?
There is a risk of post-operative apnoea and myocardial suppression with anaesthesia if:
• The pH is more than 7.5,
• The chloride is less than 95mmol/L,
• The serum bicarbonate is more than 30mmol/L.
What are the approaches for the open surgery in hypertrophic pyloric stenosis?
The open approach can be via:
• A peri-umbilical incision,
• An upper midline incision,
• A right upper transverse incision.
Why is the laparoscopic approach preferred for surgery in hypertrophic pyloric stenosis?
The laparoscopic approach is now preferred due to better cosmesis (cosmetic results).
What is done during the pyloromyotomy procedure?
The pylorus muscle is divided along the length of the ‘olive,’ leaving only the mucosa intact. This allows the pyloric canal to open up and allows milk feeds to pass through.
What are potential complications after pyloromyotomy surgery?
Potential complications include:
• Perforation of the mucosa, especially at the duodenal side of the myotomy.
• An incomplete myotomy that may require a redo operation.
What is the typical outcome for babies after surgery for hypertrophic pyloric stenosis?
These babies usually do very well. Most are on full feeds and discharged within 24 hours of surgery and return for a follow-up appointment having regained most of their weight.
What complications can arise in the post-operative period of hypertrophic pyloric stenosis surgery?
There is a small incidence of wound sepsis or dehiscence due to the malnourished status of the baby at the time of surgery.
What should be monitored in severely malnourished infants after surgery for hypertrophic pyloric stenosis?
Severely malnourished infants should be monitored for metabolic and electrolyte derangements due to “refeeding syndrome,” particularly potassium, phosphate, and magnesium deficiency.
